Prep the pan and oven: Heat the oven to 425°F (220°C). Line a large sheet pan with parchment paper. Lightly brush the paper with 1 tablespoon olive oil.
Mix the binder: In a large bowl, stir together breadcrumbs, milk, and egg.
Let it sit for 2–3 minutes so the crumbs absorb the liquid.
Add flavor: Mix in grated onion, garlic, parmesan, parsley, Italian seasoning, salt, pepper, and any optional red pepper flakes or lemon zest.
Add the chicken: Add the ground chicken. Using a fork or your hands, gently mix just until combined. Do not overwork or the meatballs will be dense.
Shape the meatballs: With damp hands or a small scoop, form 1 1/2-inch balls (about 20–24 meatballs). Place on the prepared pan with a little space between each.
Oil and bake: Brush the tops with the remaining 1 tablespoon olive oil.
Bake for 12–15 minutes, until the centers reach 165°F (74°C).
Optional browning: For extra color, switch the oven to broil and cook 1–2 more minutes, watching closely.
Serve your way: Toss with warm marinara over pasta, glaze with a little honey and hot sauce, or squeeze fresh lemon over the top with a handful of herbs.